1. Field of the Invention
The present invention relates, generally, to connecting rod assemblies and, more specifically, to a method of manufacturing a connecting rod assembly for an internal combustion engine.
2. Description of the Related Art
Internal combustion engines known in the related art may generally include, among other basic components, an engine block having one or more cylinders, cylinder heads associated with the engine block, pistons supported for reciprocal movement in each cylinder, and connecting rod assemblies to transfer the movement of the pistons to the crankshaft. The piston generally includes a bore that corresponds to a similar pin bore at one end of the connecting rod assembly. A pin is placed through the corresponding bores to attach the piston to the connecting rod assembly. The end of a connecting rod assembly having the pin bore is commonly referred to as the “small end.” The other end of a connecting rod assembly is fastened to the crankshaft at a particular location. This end of the connecting rod assembly is commonly referred to as the “crank end” or “large end.”
Generally, fuel is combusted within the cylinders to reciprocate the pistons. The piston drives the connecting rod assembly, which drives the crankshaft, causing it to rotate within the engine block. Specifically, as fuel is combusted within the cylinder, the combustion pressure drives the piston downward in a substantially linear motion, which in turn drives the connecting rod assembly in a substantially linear, but slightly rotational motion. On the other hand, the large end of the connecting rod assembly is attached to the crankshaft, which drives the large end of the connecting rod assembly in a substantially rotational motion.
Since it is the connecting rod assembly that transfers the reciprocal motion of the piston into the rotational motion of the crankshaft, the connecting rod assembly incurs a high level of stress at both the large end and small end pivot points. At the small end, the lower surface of the pivot point has to resist a high load from the transfer of the combustion pressure from the piston pin down through the connecting rod. The upper surface of the connecting rod at the small end has to resist a much lower load, which is the result of inertia force from the reciprocating masses during the exhaust stroke.
To optimize efficiency in this location, the small end of the connecting rod assembly may be manufactured to have a reduced width at the upper region with respect to the remaining portion of the small end. One type of connecting rod assembly that has a reduced width small end is commonly referred to as a “stepped” connecting rod assembly. Specifically, the reduced width small end of a connecting rod assembly permits a wider bearing area in the piston and increases the overall load carrying capability while minimizing the overall weight of the piston and connecting rod assembly.
However, in order to provide a stepped connecting rod assembly, a portion of the small end between the pin bore and the upper region is removed by a machining process. The machining process generates burrs along the edges, such as around the pin bore, which must be removed prior to assembling the connecting rod assembly to the piston. The deburring imposes an additional step in the manufacturing process that is costly and labor-intensive. Yet, without the deburring process, excess material along the small end may prevent proper assembly of the connecting rod assembly to the piston pin or other components of the engine. Additionally, the excess material may fragment from the connecting rod assembly during engine operation, which can cause engine failure.
In addition to providing a stepped configuration to facilitate load carrying capacity and seizure resistance, connecting rod assemblies may also employ a bushing within the pin bore of the small end to accomplish a similar objective. A bushing at this location is often constructed from a dissimilar material to that of the connecting rod assembly to reduce friction and provide smooth angular movement along the pivot point, thereby reducing scuffing which can cause engine damage. As a result, it is often desirous to employ a bushing at the small end of the connecting rod assembly. However, the addition of a bushing within the small end does not eliminate the need for the small end to undergo a deburring process after machining to provide a reduced width configuration.
Furthermore, moment forces are generated during installation of a bushing at the small end of a connecting rod assembly where the upper region of the small end has a reduced width with respect to the remaining portion of the small end. Specifically, during installation, the non-planar area around the pin bore of the stepped small end causes the bushing to shift in a manner where the bushing is no longer parallel with the pin bore. This can result in misalignment between the bushing and pin bore or deformation of the bushing, creating irregular contact between the bushing and the pin bore, which may lead to premature bushing failure. Additionally, this misalignment can translate to an irregular bushing surface that contacts the piston pin, which may promote scuffing and lead to engine damage.
Moment forces are also generated during the machining of the surface within the pin bore of the small end of a connecting rod assembly that contacts a piston pin. This is especially true where the connecting rod assembly has a stepped small end whether or not a bushing is employed within the pin bore. Specifically, the non-planar area around the pin bore of the stepped small end may permit the machining tool to shift while it is cutting and defining the contact surface. This shift has a tendency to create a concave lower surface, which reduces optimum efficiency at this pivot point. The creation of such a non-uniform contact surface may lead to premature failure of the pivot point between the contact surface and the piston pin, which can lead to engine damage.
The irregularities caused by the moment forces associated with installing a bushing in the pin bore of stepped small end of a connecting rod assembly as well as those associated with machining the contact surface in the pin bore are detrimental to the efficiency and cost-effectiveness of manufacturing connecting rod assemblies. Notably, these irregularities impose additional steps in the manufacturing process to inspect connecting rod assemblies and correct the irregularities where appropriate, which increases costs associated with additional labor, additional machining and lost manufacturing. Further, these irregularities can cause an out-of-tolerance condition, rendering the entire connecting rod assembly unusable.
As a result, there is an ongoing need in the art to improve connecting rod assemblies and the method of manufacturing connecting rod assemblies, in general. Specifically, there is an ongoing need to streamline the manufacturing process while retaining strength and acceptable product life of connecting rod assemblies having a stepped small end. Thus, there continues to be a need in the art for a method of manufacturing a connecting rod assembly that essentially eliminates the deburring process at the small end. Further, there is a need in the art to provide a method of manufacturing a connecting rod assembly that essentially eliminates moment forces that occur when the bushing is installed within the pin bore of a stepped small end of a connecting rod assembly as well as the moment forces that occur when a contact surface is machined in the stepped small end of a connecting rod assembly.